1. Field of the Invention
The Invention relates to multi-chip packages and in particular to stacked multi-chip packages. More particularly, the invention relates to a stacked multi-chip package with EMI shielding to isolate a chip in the package from electromagnetic interference, or from causing electromagnetic interference, in other parts of the package.
2. Background Information
Electromagnetic interference (EMI), also known as radio frequency interference (RFI), is caused by electromagnetic radiation and is a significant consideration in electronic circuit design. Electromagnetic radiation is emitted by electronic circuits and components carrying changing electrical signals. There are three main techniques for ameliorating or eliminating EMI. The first technique is to physically separate sensitive components from the source of any electromagnetic radiation. The second technique is to use bypass or decoupling capacitors and filters to ground unwanted interference signals. And, the third technique is to shield the sensitive or EMI generating components with a Faraday cage or enclosure.
The current emphasis in electronic circuit design is towards smaller and more powerful devices. A significant amount of work is being done in the area of multi-chip packages in which multiple integrated circuit (IC) chips are tightly packed within a small package. Within such packages physical separation of sensitive equipment and sources of electromagnetic radiation is not practical and decoupling is only partially effective. Therefore, shielding is an important solution within these multi-chip packages.
The most popular form of shielding within current chip packages is through use of a conductive can to enclose the sensitive or EMI generating component. The component is mounted on an area of a supporting substrate with a ground plane beneath it and a metal box, or other shaped, can is mounted over the component to enclose the component in a conductive enclosure. However, metal cans of this type take up considerable space on the substrate surface and tended to be not very robust often dislodging from the substrate surface due to cyclic stress loading on the solder joints holding the can to the substrate. They also present an obstacle to the flow of molding epoxy and water vapor may accumulate within the can if the electrical equipment experiences a sudden change in environmental conditions.